1. Field of the Invention
The instant invention is directed to a weatherable, heat sealable membrane and waterproof coverings made from said membrane. The membrane is made from elastomeric compositions produced by extrusion or calendering. The membrane may be unsupported or supported.
2. Description of the Prior Art
A recently emerging trend in the field of roofing is the displacement of the familiar built-up asphalt roofing with membrane roofing. Advantages of the new systems include ease of installation, a safer working environment for the applicator, greater resistance to cold cracking and longer term leak protection.
Another leading growth area is the utilization of ponds and pits for disposal of wastes of chemical plants, petroleum refineries, power plants and mining installations. To insure against seepage of aqueous wastes, liners must be provided. Thus, the development of pond and pit liners is a growing industrial concern.
Two membrane types, elastomeric and thermoplastic, are utilized in this new technology. A leading elastomeric membrane is vulcanized EPDM while an example of a thermoplastic membrane is plasticized PVC.
Both membrane types have advantages and disadvantages. Vulcanized EPDM has outstanding resistance to outdoor weathering, good cold flexibility, high strength and excellent elongation. Its major disadvantage is the necessity of using adhesives for seaming the membrane to provide a continuous leak-free roof covering. Such adhesives are expensive and time-consuming to apply and are prone to delaminate under stressful conditions because of their low strength. This leads to leaks. Plasticized PVC offers surer seams because the material, being thermoplastic, can either be heat sealed or solvent welded to give an integral seam of high strength. Such membranes, however tend to lose plasticizer with time resulting in short useful life and poor cold crack resistance.
In recent years, new classes of polymers have been developed which are based on chemically modified elastomers especially saturated backbone elastomers such as EPDM and Butyl rubber. More specifically, the polymers are modified in such a way as to introduce an ionic group on the polymer. Thus, they may be referred to in general as "ionomers."
Among this new class of "ionomers" are sulfonated elastomers and carboxylated elastomers. These polymers are derived from polymeric materials having olefinic unsaturation, especially elastomeric polymers such as EPDM rubber. U.S. Pat. No. 3,642,728, incorporated herein by reference, teaches a method of selective sulfonation of olefinic unsaturation sites of an elastomeric polymer to form an acid form of a sulfonated elastomeric polymer. The olefinic sites of the elastomeric polymer are sulfonated by means of a complex of a sulfur trioxide donor and a Lewis base. The SO.sub.3 H groups of the sulfonated elastomer are readily neutralized with a basic material to form an ionically crosslinked elastomer having substantially improved physical properties over an unsulfonated elastomer at room temperature. However, these ionically crosslinked elastomers may be processed like a conventional thermoplastic at elevated temperatures under a shear force in the presence of selected preferential plasticizers which dissipate the ionic associations at the elevated temperatures thereby creating a reprocessable elastomer.
The basic materials used as neutralizing agents are selected from organic amines or metallic bases in which the metal ion is selected from Groups I, II, III, IV, V, VIB, VIIB and VIII of the Periodic Table of Elements and mixtures thereof.
A further development of sulfonated polymers is provided by U.S. Pat. No. 3,836,511, incorporated herein by reference, which teaches an improved process for the sulfonation of the olefinic sites of the elastomeric polymer. The patent discloses the use of an improved sulfonating agent selected from acetyl sulfate, propionyl sulfate and butyryl sulfate. The neutralizing agents employed to neutralize the acid form of the sulfonated elastomeric polymers are organic amines.
A still further development of these sulfonated polymers is furnished by U.S. Pat. No. 4,222,914, incorporated herein by reference, which teaches a further improved process for the sulfonation of the olefinic sites of the elastomeric polymer and subsequent neutralization of the resulting polymer sulfonic acid to form a zinc sulfonate. The patent describes the reaction of a cement of the polymer with an acyl sulfate followed by neutralization with a solution of zinc acetate dissolved in methanol or methanol/water.
Another still further improvement in this class of sulfonated polymers is provided by U.S. Pat. No. 3,870,841, also incorporated herein by reference. This patent teaches a method for plasticization of the polymeric backbone of a neutralized sulfonated polymer by means of a polymer chain plasticizer which is a liquid compound having a boiling point of at least about 120.degree. F. The polymer chain plasticizer is selected from a dialkyl phthalate, a process oil or an organic acid ester.
A more recent development in sulfonated polymers is disclosed in U.S. Pat. No. 3,847,854 incorporated herein by reference. This patent teaches a method of improving the processability of neutralized sulfonated elastomeric polymers by the addition of a preferential plasticizer which has at least one functional constituent which exhibits a bond movement whose absolute value is at least 0.6 Debyes, and must be a liquid at the desired processing temperature of the neutralized sulfonated elastomeric polymer.
A still more recent development in sulfonated polymers is disclosed in U.S. Pat. No. 4,157,992, incorporated herein by reference. This patent teaches a method of improving the weathering stability and processability of neutralized sulfonated elastomer blend compositions by the mixture of carbon black, inorganic filler and non-polar process oil.
A second new class of elastomeric "ionomers" is the class of carboxylated elastomers. These polymers are derived from polymeric materials having olefinic unsaturation especially elastomeric polymers such as EPDM. U.S. Pat. No. 3,884,882, incorporated herein by reference, describes an adduct of maleic anhydride and EPDM rubber and the resultant ionomer obtained by the reaction of the adduct with a divalent metal salt of a weak acid, the metal selected from Group II of the Periodic Table of Elements, and an accelerator having an active hydrogen atom.
Further development of these carboxylated polymers is provided by U.S. Pat. No. 3,997,487, incorporated herein by reference, which discloses an elastomeric material formed by reacting an adduct of maleic anhydride and EPDM rubber with a rosin salt of a divalent or monovalent metal.
Although these ionomers represent a significant development in the elastomeric arts, none of these advances have found application in the waterproof membrane arts. That is, none of the aforementioned disclosures, explicitly suggest, implicitly imply or make obvious their use in any application which requires a waterproof membrane, covering or the like wherein the membrane or covering requires long term exposure to the elements.